Glossary
Cladograms
Diagrams that illustrate evolutionary relationships by focusing on shared characteristics (traits) among different species, often used to hypothesize evolutionary pathways.
Example:
A cladogram for vertebrates might group birds and reptiles together based on the shared derived trait of amniotic eggs.
Common Ancestry
The principle that all life on Earth is related and has descended from a single ancestral organism or a small group of ancestral organisms over vast periods of time.
Example:
The presence of similar genes across diverse organisms, from bacteria to humans, strongly supports the concept of common ancestry.
Derived Traits
Characteristics that have evolved in a specific lineage since its divergence from a common ancestor, distinguishing it from earlier forms or out-groups.
Example:
Feathers are a derived trait in birds, distinguishing them from other reptiles that lack feathers.
Evolutionary Relationships
The connections and patterns of descent among different species, indicating how closely or distantly related they are through common ancestors.
Example:
Studying the bone structure of a whale flipper and a human arm reveals deep evolutionary relationships despite their vastly different functions.
Hypotheses
Scientific proposals or explanations that are subject to testing and revision with new evidence, a concept applicable to both cladograms and phylogenetic trees.
Example:
A newly constructed cladogram is considered a hypothesis of evolutionary relationships, which can be refined or changed if new DNA evidence emerges.
Interpreting Trees
The skill of analyzing and understanding the information presented in phylogenetic trees and cladograms, including identifying common ancestors, relationships, and evolutionary events.
Example:
Successfully interpreting trees allows a student to determine which two species are most closely related based on their branching patterns.
Molecular Data
Information derived from the analysis of DNA, RNA, or protein sequences, which is often used to construct more accurate phylogenetic trees due to its reliability.
Example:
Comparing the mitochondrial DNA sequences of different primate species provides robust molecular data for determining their evolutionary closeness.
Molecular vs. Morphological Data
The distinction between using genetic sequences (molecular) and physical characteristics (morphological) to infer evolutionary relationships, with molecular data generally preferred for accuracy.
Example:
While similar wing structures in bats and birds might suggest close relatedness based on morphological data, molecular data clearly shows they evolved flight independently.
Morphological Focus
The reliance on visible or structural characteristics of organisms, such as anatomical features, to infer evolutionary relationships, often used in constructing cladograms.
Example:
Early classifications of plants relied heavily on morphological focus, grouping species based on flower structure or leaf shape.
Nodes
Points on a phylogenetic tree or cladogram that represent a common ancestor from which two or more lineages diverged, indicating a speciation event.
Example:
A node on a tree showing mammals represents the last common ancestor of all the mammal groups that branch off from that point.
Out-group
A lineage or species included in a phylogenetic tree or cladogram that is less closely related to the group of interest, serving as a reference point to root the tree.
Example:
When studying the evolutionary relationships among different types of flowering plants, a moss species might be used as an out-group.
Phylogenetic Trees
Visual diagrams that depict the evolutionary relationships among different species, showing how they are related through common ancestry and the amount of evolutionary change over time.
Example:
A phylogenetic tree might show that humans and chimpanzees share a recent common ancestor, while both are more distantly related to gorillas.
Shared Characteristics
Features or traits that are present in multiple lineages within a cladogram or phylogenetic tree, indicating a common evolutionary origin.
Example:
The presence of a backbone is a shared characteristic among all vertebrates, indicating their common ancestry.
Speciation
The evolutionary process by which new and distinct species are formed from existing ones, typically through reproductive isolation and divergence.
Example:
The geographic separation of a squirrel population by the Grand Canyon led to speciation, resulting in two distinct species.
Speciation Mechanisms
The various processes, such as geographical, reproductive, or ecological isolation, that lead to the formation of new species.
Example:
The inability of two populations to interbreed due to different mating seasons is an example of a speciation mechanism based on reproductive isolation.
Time Scale
A feature incorporated into phylogenetic trees that indicates the chronological progression of evolution, often calibrated using fossil records or molecular clocks.
Example:
A time scale on a phylogenetic tree might show that a particular group of mammals diversified rapidly about 65 million years ago, following the extinction of dinosaurs.
Trait Tracking
The illustration within phylogenetic trees of how specific characteristics or features have been gained or lost over evolutionary time in different lineages.
Example:
A phylogenetic tree might use trait tracking to show that the evolution of flight in birds involved the gradual modification of forelimbs into wings.